“What we can tell you is that United States trade restrictions and economic sanction laws prohibit Blizzard from doing business with residents of certain nations, including Iran,” it said.

“This week, Blizzard tightened up its procedures to ensure compliance with these laws, and players connecting from the affected nations are restricted from access to Blizzard games and services.”

The statement explained that because of the terms of the US trade sanction, it would be unable to offer any refunds, credits, transfers, or other service options to accounts in Iran or other countries where similar sanctions were in place.

The US is stepping up economic pressure on Iran as it seeks more information on the country’s nuclear programme.

The move has prompted a mixed reaction from Iranian gamers, who are still able to access the game’s message boards. While some have expressed disappointment, others have posted angry criticisms of Blizzards actions.

One comment on the notice board reads: “Blizzard had full knowledge that this was going to happen. But what did they do? They continued to accept subscriptions and MoP pre orders.”

Before Blizzard’s statement, there were theories that the Iranian government itself was blocking access to popular online games. Last year, the country’s FARS news agency reported that the first-person shooter Battlefield 3 had been banned.

More recently, Iranian gamers contacted US game sites claiming that the country’s Ministry of Culture and Islamic Guidance was cracking down on all titles ‘promoting’ superstition or mythology.

Difficulties in accessing other fantasy adventure games such as the popular Guild Wars titles have also been discussed on gaming message boards.

World of Warcraft is the world’s largest subscription-based online multiplayer game, with around 10 million users. Participants pay a monthly fee to explore its vast landscapes, engaging in quests and upgrading their in-game characters.

A new update, Mists of Pandaria is due out later this year – it’s doubtful whether the game’s Iranian fans will get to see it.